This invention relates in general to medical catheters and, more particularly, to blood vessel catheters. In one aspect of the invention it relates to hemodialysis catheters.
Blood vessel catheters are normally either venous catheters or arterial catheters. Venous catheters, in turn, usually come in several forms. The simplest are short peripheral catheters. Next come midline catheters, central venous catheters and port catheters. A hemodialysis catheter is one form of central venous catheter and is normally placed in the superior vena cava. The present invention may find application in each of the aforementioned venous catheters. However, it finds particularly advantageous application in hemodialysis catheters.
Hemodialysis, as practiced today, normally employs one of two types of catheter to remove blood from the patient for processing and return processed blood to the patient. Most commonly, a catheter tube containing two lumens is used, each lumen having a semi-cylindrical configuration. This is frequently referred to as a dual lumen catheter. Alternatively, two separate tubes, each with a full cylindrical configuration, may be used to remove blood for dialysis and return the processed blood.
Hemodialysis membranes are now able to process blood at over 500 ml of flow per minute. Even higher processing rates are foreseeable. However, problems occur with both the line introducing purified blood back into the vein (the venous line) and the line removing blood for purification (the arterial line) at flow rates above 300 ml per minute. A high flow rate from the venous line can cause whipping or xe2x80x9cfirehosingxe2x80x9d of the tip in the vein with consequent damage to the vein lining. A corresponding high flow rate into the arterial line causes the port to be sucked into the vein wall, resulting in occlusion. It should be understood, of course, that both lines normally access the superior vena cava and the designations are used for differentiation purposes.
Speed of flow through a catheter lumen, whether it be in a single lumen or a dual lumen catheter, is controlled by a number of factors including the smoothness of the wall surface, the internal diameter or cross-sectional area of the tube lumen, and the length of the tube lumen. The most important factor is the cross-sectional area of the tube lumen. The force or speed of the fluid flow in a tube lumen for a given cross-sectional area is controlled by the external pumping force, of course. This is a positive pressure pushing processed blood through the venous lumen and a negative (suction) pressure pulling unprocessed blood through the arterial lumen.
Problems encountered in providing for a high flow rate through a catheter are magnified in a dual lumen catheter construction. Because each of the lumens in a dual lumen catheter has a D-shape, it has been assumed that flow rates are limited. Furthermore, such dual lumen catheters are, to a great extent, catheters with a main port which opens at the end of a lumen substantially on the axis of the lumen. Thus, firehosing frequently results. There are dual lumen catheters which utilize side ports for both outflow and inflow. An example is the catheter disclosed in the Cruz et al. U.S. Pat. No. 5,571,093. However, such catheters have not been successful in solving numerous problems related to hemodialysis with dual lumen catheters, e.g., high incidences of catheter port occlusion as well as some degree of fire-hosing still occurs.
A flow balance between the venous and arterial lines is also of obvious importance. Occlusion of the arterial line is a very common limiting factor in hemodialysis. While the venous line tends to remain clear and open, because the direction of flow forces tube ports away from the vein wall, in the arterial line this high flow tends to pull the port against the vein wall, thereby sucking the wall into the port and occluding it. Andersen et al. U.S. Pat. No. 4,594,074, Quinn U.S. Pat. No. 5,451,216, Quinn U.S. Pat. No. 5,810,787, Quinn U.S. Pat. No. 5,599,322 and Quinn U.S. Pat. No. 5,571,093 all discuss the need for improved aspiration in catheters generally.
Additionally, some key problems face dialysis clinicians using dual lumen central venous catheters or catheters placed via the jugular route. Clinicians routinely face a situation where either the venous or the arterial lines fail to function during dialysis, or when the patent is first connected to the dialysis machine. The dialysis center clinician must find a way to make the system work as he or she does not have the option of immediately changing the catheter. Failure is most often on the arterial or pulling side, where the catheter port is sucked against the vessel wall. Occlusion can also be caused by a combination of clots and the proximity of the vessel wall. The problem is frequently addressed by reversing the lines, by flushing the lines with saline and/or by repositioning the patient so that gravity can help move the catheter tip way from the vessel wall. Insofar as reversing the lines is concerned, although it can be very effective, it also may result in ineffective dialysis because venous (dialyzed) and arterial blood tend to mix more easily when venous blood is then being directed at the arterial port instead of away from it.
An object of the present invention is to provide an improved blood vessel catheter.
Another object is to provide a blood vessel catheter which substantially reduces the opportunity for occlusion to occur during outflow.
Another object is to provide an improved hemodialysis catheter which is capable of delivering processed blood to the patient at high flow rates without harmful firehosing or whipping of the catheter tip.
A further object is to provide a hemodialysis catheter which is capable of returning processed blood to the patient at flow rates of 500 ml or greater without traumatizing the patients blood vessel.
Yet a further object is to provide a hemodialysis catheter which permits high flow rates while minimizing trauma and potential red cell and platelet damage so as to avoid clotting.
Yet another object is to provide a hemodialysis catheter which permits substantially increased venous flow rates while reducing output force and increasing the diffusion rate.
Another object is to provide a dual lumen hemodialysis catheter which permits flow rates higher than the latest separate lumen catheters without harmful firehosing of the catheter tip.
Yet another object is to provide a dual lumen hemodialysis catheter which permits high flow rates while minimizing trauma and potential red cell and platlet damage so as to substantially avoid clotting.
A further object is to provide a dual lumen hemodialysis catheter which substantially reduces the incidence of arterial port occlusion.
Still a further object is to provide a dual lumen hemodialysis catheter in which flow can be reversed without significant mixing of venous and arterial blood.
Yet a further object is to provide new and improved bolus tips for dual lumen, hemodialysis catheters.
The foregoing and other objects are realized in accord with the present invention by providing a first embodiment of blood vessel catheter which combines a single lumen catheter tube and a bolus tip. The bolus tip has a bullet nose and a main side port. The catheter has at least one additional radially extending side port displaced axially from the main side port. The additional port or ports are elongated axially of the catheter so as to have a race-track shaped edge. The edge is semi-circular in cross-section.
In one form of the first embodiment, the catheter tube has an elongated cylindrical body, fabricated of thermoplastic material such as polyurethane, or thermoset material such as silicone rubber. An axial passageway or lumen extends the length of the cylindrical body, from a proximal to a distal end. The cylindrical wall which defines the lumen has an axially and circumferentially spaced series of radially extending ports formed in it adjacent the distal end. Each port is elongated axially of the body so as to have a race-track shaped edge. The race-track shaped edge is semi-circular in cross-section around its entire length.
Directly opposite each port in the body of the tube, the body wall is thickened in an oval pattern to form a longitudinally elongated dimple. The dimple forms a stiffening arch in the tube wall. The arch serves to prevent the tube from buckling at the port.
The distal end of the tube has a bolus tip. The bolus tip is a separate element. It is molded of the same resilient plastic. The tip may be glued or welded to the distal end of the tube. It may also be insert molded on the tube.
The bolus tip has a tube connector section adjacent the distal end of the tube, a bullet nose section and a passage section between the tube connector section and the bullet nose section. The passage section of the bolus tip has an axial passage in it adjacent the connector section and a radial passage adjacent the nose section. The axial passage is in fluid communication with the tube lumen. The radial passage leads to a main port extending radially through the side of the bolus. The main port extends circumferentially around slightly more than 180xc2x0 of the bolus, i.e., about 190xc2x0.
In another form of the first embodiment, the passage section of the bolus is extended and a second port is formed in the side of this passage section. The second port is displaced 180xc2x0 around the axis of the bolus from the main port in the bolus. Directly opposite the second port, the passage section wall is thickened to form a longitudinally elongated dimple. A third port axially aligned with the main port and 180xc2x0 and displaced from the second port may also be used. The passage section wall is also thickened to form a longitudinally elongated dimple opposite the third port.
The dimple opposite the second port stiffens the bolus at the second port and tends to hold the main port away from the vein wall. As such, it aids in preventing occlusion of the main port and, also, protects the vein wall from abrasion by the edge of the main port.
In a conventional single lumen hemodialysis catheter, for example, substantially the full pumping force is directed axially out of the end of the catheter because of its end port orientation and the size and shape of any side ports employed. Little flow is directed through such side ports. The aforedescribed embodiment provides a side port or ports which allow higher flow rates. This redirection of flow through a longitudinally elongated side port or ports separated from the main side port in the bolus reduces the speed or force of flow from each port. This reduction in force results in better diffusion and protects against whipping. In addition, the port configurations are smoother and have no sharp edges to damage blood cells. During arterially or inflow to such a catheter, clogging and occlusion due to xe2x80x9cvein wall suckingxe2x80x9d is substantially avoided.
A second embodiment of hemodialysis catheter includes a dual lumen catheter tube and bolus. The bolus has a main outflow or venous port. At least one intake or arterial port extends radially through the bolus or the tube.
In one form of the second embodiment, the arterial and the venous lumens open through a radially extending main venous port and a main intake or arterial port which are immediately adjacent each other on one side of the bolus next to the bullet nose in the bolus. The venous lumen also opens through a second outflow port formed in the tube adjacent the bolus and circumferentially displaced 180xc2x0 around the axis of the catheter tube from the main venous port. Directly opposite this second venous port, which is longitudinally elongated, the tube body wall is thickened in an oval pattern to form a longitudinally elongated dimple. The dimple forms a stiffening arch in the tube wall and prevents buckling of the tube at the second venous or outflow port.
In another form of the second embodiment, the venous and arterial lumens open through radially extending, axially displaced main outflow and intake ports on the same side of the catheter bolus. A main outflow port for the venous lumen port is formed radially in the bolus adjacent its bullet nose. A second outflow port for the venous lumen is formed radially in the bolus, circumferentially removed 180xc2x0 from the main port and displaced axially from the main port. A third outflow port is formed radially in the bolus, axially aligned with the main outflow port and axially displaced from both the main and second outflow ports. A main inflow or arterial port is formed radially in the bolus at a point axially displaced in the bolus from the outflow ports.
In this form of the invention, directly opposite each of the second and third outflow ports and the main intake port the tube body wall is thickened in an oval pattern to form a longitudinally elongated dimple. Each dimple forms a stiffening arch in the bolus and prevents buckling of the bolus at the corresponding ports.
In this form of the invention also, the dual lumen tube is preferably a 13.5 French tube, giving it a nominal O.D. of 0.180 inches. The bolus tip, on the other hand, is 10 French size, i.e., it has a nominal O.D. of 0.136 inches. The bolus tapers from the 13.5 French size to the 10 French size between the second and third ports. As such, the inflow lumen has a D-shape until it reaches a tapered middle of the bolus, whereupon it transitions to a circular cross-section. At the same time the cross-sectional area of the lumen increases from about 0.005 in2 to about 0.006 in2. This form of bolus is 1.62 inches long.
In a variation of this form of bolus, the bolus body is shorter, being only 1.46 inches long. This is achieved by shortening the transition sub-section of the bolus body (between the 13.5 French and 10 French diameters) and moving the second and third venous ports closer together. The stiffening arch beneath the third venous port is eliminated and the transition section thickness serves the same purpose. The shorter bolus body is even less likely to kink under bending stress.
In another variation of this form of the invention, the venous and arterial ports are displaced 180xc2x0 from each other about the axis of the bolus. As a result, even when flow is reversed from its normal pattern, no significant mixing of venous and arterial blood flow results. The outflow diversion and dispersion characteristics of the venous and arterial ports arranged in this way assures that venous flow from the upstream port (normally arterial) will flow past the (then) arterial port without any significant mixing taking place.